BSpline BRep Faces

Faces are parametrized with two parameters (u and v). Ranges of the u,v
parameters (parameter rectangle) are specific to each patch

A face can be closed in one (a cylinder) or both (torus) directions.

With the simple (natural) parametrization above a face is a deformed and
stretched rectangle. To model more complicated patches like triangular or
polygonal curved patches or patches with holes a face can have trimming wires
applied to the surface of the natural patch. For example a rectangle with a hole
has two wires: The external (natural) one and internal trimming wire, defining
edge of the hole.